Thanks Al
Maybe it is some other product they have in mind. In the downloadable Instruction P.38 it says:
"Finally make sure you do not use a wet premixed fireplace mortar with water soluble binder ..."
I can't tell whether that is applicable to the product I linked but for sure none of the options they recommend are wet premix - but your post sure reassures me thanks a lot
Aidan

Hi Sharkey - sorry I missed your post the last time I looked in here - thanks for the reply.

It seems my problem was just that I had set my arch height 3" higher than my arch radius at 13.5" in and with a dome size of 39" and with a brick of the standard size it just wouldn't work with the IT set on the dome floor. I now see that if the arch is set higher than the radius then to measure consistently with the "IT" the IT centre should be set at a height equal to the difference between the height wanted and the arch radius. So if I want an arch of 13.5" high with an arch radius of 10.5" I should set the IT during building up to that at 3" above the floor.

I tried out this principle and it seems to work out all right.
First I reduced the height to a more appropriate height of 12" and now with an arch radius of 10.5" I can cut a set of identical bricks for my arch. Until I reach the top of the arch I will raise the IT 1.5" above the dome floor (to get the 12 " height and that should ensure that the dome walls and the arch coincide. I will also have a soldier course of half bricks (4.5") surrounding the floor (which will add 1.5" above floor level (3") to the bottom of the hemisphere.
I really must start my own thread Aceves sorry.
Is my assumption correct that the arch bricks in a construction such as yours GianniFoccacias and KaragiDudes could or should in theory be identical and cut from a template as shown in the sketch. I have cut one arch brick and set up a test and it seems to work OK anywhere in the arch - as measured with the IT. In the sketch I have just allowed for the arch face to project just 1" outside the dome. Is there ay reason it should be more (or less?). The inner face works out at 2.5" and and the arch itself at 3.75".

The arch bricks are NOT the same size or angles. If you make them the same size your dome will have to be teardrop shaped in order for the dome to reach the top of the arch.

The idea is that the inner face of the arch brick (the one labelled as 2.5” in your drawing) is part of the inner dome wall. As such, the angle of this changes as you come up the arch and can be found using the end of your indispensable tool.

To achieve this you also need the arch to reach into the dome as you come up. i.e., the bricks get longer. The top edge (labelled 1” ) and the bottom edge (labelled 3.75” in your drawing ) will have to be increasingly longer as you get higher up the arch. The first photo is about the only photo I have that shows this, but you can see that the arch bricks are getting deeper as you come up the arch so that the inner edge of the arch matches the curve of the dome.

I sat each arch brick in one at a time with appropriate spacers. I first marked the length the brick needed to be using the indispensable tool. This is the red line I have marked on the copy of your drawing in the second photo. I cut this and then placed the brick back and again used my tool to mark the angle of the second cut - the green line in the drawing. This is just at the point where the angle of the tool makes a 4.5” face. You can trace the top side of one arch brick onto the bottom of the next arch brick and then use the same method to mark the top again.

Thanks again for taking the trouble to reply. I know what you mean when you say:

"To achieve this you also need the arch to reach into the dome as you come up. i.e., the bricks get longer"

I agree if you have a hemisphere and you want an opening which "higher" than a semicircle you will get that effect. But what I was trying to say - not very well maybe - was that there is a way to get identical cuts on all arch bricks.

I didn't maybe explain it very well but actually I do believe it does work as I said above. I'll try to explain it this way. If the dome is a hemisphere and the opening arch is semicircle then it must work out OK since all points on the arch inner edge are equidistant (a dome radius) from the centre of the dome. also all points on the 2.5" circle surrounding this are also a radius distance from the dome centre.

If you agree that it works for hemisphere dome and semicircular arch then my proposed way to increase the height is this.

Say you want an extra 1.5" height in the opening arch.

Raise the dome hemisphere 1.5" by just using a higher soldier course. Now you still have a hemisphere but it is sitting on top of a 1.5" cylinder.

Raise the IT at the dome centre also 1.5" . This is the key I believe.

Build the dome up to above the arch in the normal way. If you keep going to the top the dome height will be 1.5" above the desired. But you could also reel in this a bit over the top rows by shortening the IT

Actually in theory you could have an opening any height so long as you just folllow those last two points - and have enough bricks the opening width remains the same, but every brick in the opening should be identical.

I'll try to show by a sketch again. I have also done a detailed explanation but it's too long and I'll post it on a separate thread which I will start soon.

BtW I had another look at your dome - fantastic location and well built. I haven't laid a brick yet but I'm alraedy using up Aceves thread
regards
Aidan

Amac,
Each arch brick is at a different height since it is an arch. The angle on the brick is a function of the height, so I don't see how the bricks in the arch can be the same.
I look forward to seeing the detailed explanation.
Jeff

Amac,
Each arch brick is at a different height since it is an arch. The angle on the brick is a function of the height, so I don't see how the bricks in the arch can be the same.
I look forward to seeing the detailed explanation.
Jeff

Hi Jeff

I will do that later - it was more of an explanation to myself as a lot of it is obvious, First though I will show two pictures I made of a dry run to test the theory, It should convince you that these "rules" apply.

1. All the bricks in the arch can be identical.
2, The angle of the cut will always be 90 degrees. In the pictures that is the angle held by the IT.
3. The face of the bricks which attach the arch to the dome will always be half a brick - or in my case 4.5"
4. The arch will project outside the dome for exactly the same distance all round. This distance is flexible and can be 0. This projection will also determine the thickness of the arch at the opening.
5. The arch will be vertical. There is no limit to the height you can go (within reason of course or we could end up with the "leaning tower of Pizza" ) provided you keep the IT and dome elevation the same.

The pictures show a soldier course of 1/2 bricks 4.5" high. The IT is resting on bricks laid on their edges, so also 4.5" high. I have cut just 1 brick for the arch so far and placed it on the arch extremes. I also tried it at other angles (no pictures) but it works there also. I just had to rotate the IT a half turn to show the first brick. My arch mould is semicircular 21" radius. The soldier course is set out for 39" radius

You can easily imagine that the soldier course (and the IT) could be a full brick high - or two bricks etc. Just keep the hemisphere on top and the semicircular arch and the "rules" above apply

BTW the wooden item in the background I used to mark the brick for cutting (I am getting a lot of use from those floorboard cutoffs. You can see it is the same shape as the cut brick - and can be used to mark both sides. The "platform" butts up to the brick and can be slid along if you want more projection.

Sharkey is correct. The arch bricks are not the same nor are their angles. You are faced with intersecting a plane (arch) with a sphere. As a dome progresses upward the circumference decreases and the interior profile angle gets shallower. Therefore you must make adjustments to each brick for each course.

Most builders follow the FB plans and build their inner arch with identical bricks in a perfect plane (inside and out). This is by far the easiest and quickest construction method. A few (Sharkey, Karangi Dude) improved on this design and cut their arch bricks to accept adjoining dome bricks uniformly and avoid the dreaded overhanging bricks and resulting gaps. I believe this configuration is also stronger than the FB design.

It is fairly easy to build an arch that matches the interior circumference of the dome over the first three or four relatively vertical courses. The challenge is to angle the interior face of each arch brick to remain consistent with the interior of the dome, both the circumference and the profile.

The following pics (especially the Oyster Bar) illustrate that all of the bricks cut in this fashion are different. Despite the appearance of being the same (pic #4) note that the interior faces are different not only in height, but that they are not true trapezoids either.

Hi Gianni
Thanks again for that reply. BTW that image - 5th pic - is not clear since it seems to not be expandable.

In any case I am not sure if you disagree with my starting point that all bricks on a semicircular arch on a hemispherical dome, should be identical in shape and interchangeable, or whether it is my proposed method to add height to the arch while still retaining this property?

As you might be able to tell I am still not convinced I am wrong. I told the missus that the "dome community" disagreed with my theory and she said "maybe they don't realise yet that you are always right"
Irony is that it was pics of your dome which first convinced me, and now I can't be unconvinced. Let me know the answer to the question above and I will try to explain my "proof" in more detail.
regards
Aidan
Sorry again Aceves!

No worries about highjacking the thread! If posting on my thread presents and solves a building problem, then it's all good! I would be worried if you were all posting about things unrelated to my thread, WFO building, or Forno Bravo in general. Then I would have to step in and ask you to please stop. But so far, the discussion's been very interesting!

Amac, as to your specific question and "rules," I'm going to have to side with Gianni, Sharkey and PizzaIdiot. They are correct on this one. I say this because I've been in your shoes. I was "convinced" that all my arch bricks would be cut the same and that the dome would meet up with them in a beautiful, flawless connection.

Not so. After I finished my arch and started to build my dome, I realized that my top arch bricks were 1) not long enough, and 2) needed different angled cuts as the arch went up. In theory, I assumed it would work. In reality, it didn't work as well as I had hoped. I had to compromise a few cuts and modify a few dome bricks to prevent the "dreaded droop" as much as possible, but I still got a little droop at the very top of the arch.

Once I cleared the dome/arch transition, I was able to regain my perfect dome rows and continue with no droop until I closed my dome with a custom-cut dome keystone.

I could not see this until I actually started building, so I suspect that you will not be convinced otherwise by any one of us until you see it and experience it yourself.

My suggestion: you build and move ahead with your cuts, and when your dome reaches the top of the arch, you will "see" the light, and realize that these builders knew a thing or two. I don't mean to say this in a mean-spirited way - not at all; i'm only saying this because this is exactly what I had to go through to understand what they were saying about the arch angles and dome slope.

My suggestion to go ahead is backed by my own build: even though I cut all my arch bricks exactly the same, and they came up a little short at the top, I still was able to adjust my dome for my short bricks and build a nice dome/arch transition. So, it can be done!!

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